Combustion furnaces for burning pulverized fuel such as pulverized coal fed from powder supply devices are known as combustion furnaces used in blast furnace facilities, thermal power plants, and the like. In such a combustion furnace, pulverized fuel is sprayed thereinto together with air and burnt therein. Such a burning method using pulverized coal is widely used for reasons such as the economical efficiency of coal, which is higher than those of petroleum and LPG.
A gas-carried powder supply device that conveys pulverized fuel with carrier gas is known as a powder supply device for supplying pulverized fuel to the combustion furnace. In such a powder supply device, the pulverized fuel in a feed tank is fed to a powder delivery pipe and conveyed by the carrier gas therein. In general, the supply rate of the pulverized fuel into the powder delivery pipe is controlled according to the aperture of a valve for powder provided at an outlet in a bottom portion of the feed tank and the differential pressure between the pressure in the feed tank and the pressure in the powder delivery pipe (see, for example, Patent Document 1 below).
The amount of the pulverized fuel to be fed into the powder delivery pipe is adjusted on the basis of values detected by a plurality of instruments. Examples of such instruments include a load cell (a weighing scale) that measures the weight of the feed tank. The amount of the pulverized fuel to be fed into the powder delivery pipe is adjusted with a load cell in the manner described below. The weight of the powder in the feed tank is obtained from the weight of the feed tank measured by the load cell, and the change in the weight of the powder is differentiated to obtain the rate of change in powder weight. The supply rate per unit time of the pulverized fuel fed into the powder delivery pipe is computed from this rate of change in powder weight. Then, on the basis of the result of this computation, the aperture of the valve for powder and the differential pressure between the inside of the feed tank and the powder delivery pipe are adjusted to adjust the supply rate of the powder.
From the viewpoint of the adjustment of the supply rate of the powder in this manner, it is important to correctly obtain the weight of the powder in the feed tank from a measurement taken with a load cell.